SAE J300
Viscosity standard for automotive engine lubricants
SAE J300 is a standard that defines the viscometric properties of mono- and multigrade engine oils, maintained by SAE International. Key parameters for engine oil viscometrics are the oil's kinematic viscosity, its high temperature-high shear viscosity measured by the tapered bearing simulator, and low temperature properties measured by the cold-cranking simulator and mini-rotary viscometer. This standard is commonly used throughout the world, and standards organizations that do so include API and ILSAC, and ACEA.
The SAE has a separate viscosity rating system for gear, axle, and manual transmission oils, SAE J306, which should not be confused with engine oil viscosity. The higher numbers of a gear oil (e.g., 75W-140) does not mean that it has higher viscosity than an engine oil 20W-50.
Grades
In the SAE J300 standard (2021), the viscosity grades are 0W, 5W, 10W, 15W, 20W, 25W, 8, 12, 16, 20, 30, 40, 50, and 60. In the United States, these numbers are often referred to as the "weight" of a motor oil, and single-grade motor oils are often called "straight-weight" oils. The grades with a W designation are considered Winter-grades, and denote an engine oil's low-temperature properties, while non-winter grades denote an engine oil's properties at the operating temperature of an engine. The SAE 8 through SAE 16 viscosity grades describe oils that can improve fuel economy through reduced hydrodynamic friction.
To assign winter grades, the dynamic viscosity is measured at various cold temperatures, specified in J300, in units of mPa·s, or the equivalent older non-SI units, centipoise (abbreviated cP), using two test methods. They are the cold-cranking simulator (CCS, ASTM D5293) and the mini-rotary viscometer (pumping, ASTM D4684).
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